This grant will support the continued development of a Human Twin Panel at the Medical College of Virginia to be used for a wide variety of clinical studies. The genetic control of continuously distributed metric traits will be investigated using a new model for the analysis of quantitative inheritance that involves the study of the descendants of monozygotic twins. The model will be extended to qualitative traits in a collaborative study with scientists at the University of Oslo in which reproductive histories will be obtained from twin pairs in the Norwegian twin registries. Newborn twins will be identified and studied in systematic manner to learn more about the biology of twinning. The primary twin rate in twin prone women will be determined by ultrasound examinations during early pregnancy. A population based registry of Virginia born twins will be developed by the ascertainment of twins through birth records. New methodologies for the use and analysis of twin data including the co-twin control technique will be developed and implemented.